Integrated optical module including a waveguide and a photoreception device

ABSTRACT

An optical module includes support substrate, an optical waveguide on the support substrate, a photoreception device on the support substrate, an optical path conversion part for converting an optical path of an optical beam guided through the optical waveguide from a first optical path to a second optical path that leads to a photodetection area of said photoreception device, wherein the optical path conversion part is provided on the photodetection device as a part thereof, such that the optical beam emitted from the optical waveguide impinges upon the photodetection area of the photoreception device.

This is a divisional of application Ser. No. 08/552,474 filed Nov. 9,1995, now U.S. Pat. No. 5,701,374.

BACKGROUND OF THE INVENTION

The present invention generally relates to optical semiconductor devicesand more particularly to an integrated optical module that includes aphotoreception device and an optical waveguide integrated with eachother.

Semiconductor photodetection devices are indispensable in opticalinformation processing systems for use in the field of so-calledmultimedia where image data and audio data are processed as a part ofthe information signals processed by the system. In such opticalinformation processing systems, it is essential to achieve efficientoptical coupling between an optical waveguide used for transmittingoptical signals and a photoreception device used in an optical modulefor detecting optical signals transmitted through the optical waveguide.

On the other hand, in order that such multimedia is accepted widely byhuman society, it is necessary to provide the optical processing systemswith low cost while achieving efficient optical coupling between theoptical waveguide and the corresponding photoreception device.

FIG. 1 shows the construction of a conventional photodetection moduleproposed previously by the inventor of the present invention.

Referring to FIG. 1, the photodetection module is constructed upon asupport substrate 1 that carries thereon wiring patterns 1a and 1b,wherein the wiring patterns 1a and 1b are connected to a semiconductorphotoreception device 10 mounted upon the support substrate 1 by way ofa flip-chip process.

The photoreception device 10 includes a substrate 2 of n-type InP onwhich a buffer layer 3 of n-type InP is provided, wherein the bufferlayer 3 carries thereon an undoped layer 4 of InGaAs and a layer 5 of n⁻-type InP formed on the InGaAs layer 4. Further, p-type diffusionregions 5a and 5b are formed in the foregoing InP layer 5. As a result,it will be noted that pin diodes D1 and D2 are formed in correspondenceto the diffusion regions 5a and 5b.

FIG. 2 shows an equivalent circuit diagram of the diodes D1 and D2.

Referring to FIG. 2, it will be noted that the diodes D1 and D2 areconnected in series via the n-type InP layer 3 with mutually opposingpolarities, wherein the diode D1 forms a drive circuit that drives thediode D2. More specifically, the diode D1 causes a reverse biasing inthe diode D2 when the diode D1 itself is forward biased, wherein thediode D2 thus reverse biased in turn causes a conduction in response toan incident optical beam. In other words, the diode D2 acts as aphotodiode. It should be noted that the p-type region 5a correspondingto the drive diode D1 has a substantially larger area than the p-typeregion 5b forming the photodiode D2. Thus, the drive diode D1 can supplya large drive current to the photodiode D2. Associated with such a largearea of the p-type region 5a, the drive diode D1 has a large junctioncapacitance Cp, while the photodiode D2 has a very small junctioncapacitance associated with the small area of the p-type region 5b.Thus, the photodiode D2 shows a very high response against incidentoptical beam.

In the photoreception device 10 of FIG. 1, it should be noted that thesubstrate 2 carries a microlens 2a on the rear side in correspondence tothe foregoing photodiode D2, such that the optical beam incident to therear side of the substrate 2 from an optical fiber 11 is focused upon apart of the InGaAs layer 4 located above the p-type region 5b. Further,the photoreception device 10 includes an insulation film 6 covering thesurface of the n-type InP layer 5, wherein the insulation film 6 isformed with contact holes 6a and 6b respectively in correspondence tothe diffusion regions 5a and 5b. Further, metal bumps 7a and 7b areformed on the diffusion regions 5a and 5b respectively in correspondenceto the contact holes 6a and 6b. Thereby, the photoreception device 10 ismounted upon the support substrate 1 in an inverted or turned-over stateby way of a flip-chip process to form the photodetection module, and themetal bumps 7a and 7b are connected electrically as well as mechanicallyto the foregoing conductor patterns 1a and 1b on the support substrate1.

In the illustrated construction, it should be noted that anotherconductor pattern 1c is provided on the rear side of the supportsubstrate 1 in electrical connection with the conductor pattern 1a or 1bby way of a via hole 1d, wherein the conductor pattern 1c is connectedto a d.c. current source 12 that supplies a positive voltage. Further,an output terminal and a load resistance R_(L) are connected to theconductor pattern 1b. As a result, a circuit is formed as indicated inFIG. 2 in which the diode D1 is forward biased and the photodiode D2 isreversely biased. In FIG. 1, it should further be noted that the rearside of the InP substrate 2 carries an anti-reflection film 8.

In the construction of FIG. 1, the photoreception device 10 is mountedupon the support substrate 1 with low cost and with reliability byemploying the flip-chip process. Thereby, the fabrication cost of thephotodetection module is reduced substantially. Further, by reducing thearea of the diffusion region 5b that forms the essential part of thephotodiode D2, the response of the photodiode D2 is improvedsubstantially. Further, such a construction of FIG. 1 is advantageousfor eliminating mechanical stress from being applied to the activeregion of the photodiode D2 which is essential for the detection of theincident optical beam. In the structure of FIG. 1, most of the externalmechanical stresses applied to the module is absorbed by the diffusionregion 5a of the drive diode D1 that has a much larger area than thephotodiode D2.

On the other hand, the photodetection module of FIG. 1 has a drawback inthat it is necessary to provide a separate holding mechanism for holdingthe optical fiber 11 in alignment with the microlens 2a on the substrate2, while such a holding mechanism has to be adjusted for each of thephotoreception devices 10 such that an optimum optical coupling isachieved between the core of the optical fiber 11 and the microlens 2a.As the core of an optical fiber has a diameter of about 6 μm at best,such an adjustment of the holding mechanism of the optical fiber 11takes a substantial time. It should be noted that the adjustment of thefiber holding mechanism has to be made by monitoring the output of thephotodiode D2 in search of the optimum position where the output of thephotodiode D2 becomes maximum. Thereby, because of the long time neededfor the adjustment, the fabrication cost of device increases inevitablyin the optical module of FIG. 1.

On the other hand, there are proposals for optical modules that does notrequire such a holding mechanism of optical fiber as indicated in FIG.3, wherein those parts corresponding to the parts described previouslyare designated by the same reference numerals and the descriptionthereof will be omitted.

Referring to FIG. 3, there is provided an optical waveguide 13 on theupper major surface of the support substrate 1, wherein the opticalwaveguide 13 is formed monolithically upon the substrate 1 and includesa waveguide layer 13c sandwiched vertically by a pair of cladding layers13a and 13b. Further, a mirror element 14 having a mirror surface 14a isprovided in the path of the optical beam emitted from an edge surface13A of the foregoing waveguide layer 13c. It should be noted that themirror element 14 has a lower major surface contacting to the uppermajor surface of the support substrate 1 and an upper major surfaceparallel to the foregoing lower major surface, and the photoreceptiondevice 10 is carried upon the upper major surface of the mirror element14.

In such a construction, the optical beam guided through the opticalwaveguide 13 and emitted from the edge surface 13A, is reflected by themirror surface 14a and impinges upon the rear surface of the substrate 2of the photoreception device 10, wherein the optical beam thus enteredinto the substrate 2 reaches the active region of the photodiode D2 thatcorresponds to the diffusion region 5b.

Thus, by providing the mirror element 14 at a predetermined position ofthe support substrate 1 and by providing the photoreception device 10 ata predetermined position of the upper major surface of the substrate 1,it is possible to achieve an optical coupling between the opticalwaveguide 13 and the photodiode D2 of the photoreception device 10easily, by merely aligning the photoreception device 10, the mirrorelement 12 and the optical waveguide 12 with each other on thesubstrate 1. It should be noted that such a positional alignment may beachieved easily by forming alignment marks on the substrate 1 or on themirror element 14.

The construction of FIG. 3, however, has a drawback in that it requiresthe mirror element 14 as an additional component. Associated with this,the construction of FIG. 3 requires additional fabrication steps.Further, use of such a mirror element 14 tends to cause modification ofthe optical beam path in the optical integrated circuit. In order toachieve an optimum optical coupling between the photodiode D2 and theoptical waveguide 13, it is necessary to adjust both the mirror element14 and the photodetection device 10 with respect to the opticalwaveguide 13, while such an adjustment is extremely difficultparticularly when the precision of the mirror element 14 isinsufficient.

Further, use of such a mirror element 14 in the optical path of theoptical beam tends to increase the optical path length of the opticalbeam emitted from the edge surface 13A of the optical waveguide 13. Whenthe optical path length of the optical beam is increased, the opticalbeam experiences a substantial beam divergence when it reaches theactive region of the photodiode D2. In such a case, it is necessary toincrease the size of the active region of the photodiode D2 incorrespondence to the increased beam diameter of the optical beam, whilesuch an increase in the size of the active region of the photodiode D2invites an increase in the junction capacitance of the diffusion region5b that forms the active region of the photodiode D2. Thereby, theresponse of the photodiode D2 is inevitably deteriorated. When the sizeof the active region 5b of the photodiode D2 is to be set small formaintaining high response speed, on the other hand, the efficiency ofoptical coupling of the photodiode D2 is degraded substantially due tothe fact that most part of the optical beam from the optical waveguide13 misses the active region 5b of the photodiode D2.

FIG. 4 shows the construction of another conventional photodetectiondevice, wherein those parts described previously are designated by thesame reference numerals and the description thereof will be omitted.

Referring to FIG. 4, it will be noted that the photoreception device 10is now flip-chip mounted directly upon the upper major surface of thesupport substrate 1 that carries also the optical waveguide 13 thereonas an integral, monolithic body. In such a construction, the edgesurface of the active layer 4 formed on the InP substrate 2 faces theexposed edge surface 13A of the waveguide layer 13c, and the opticalbeam emitted from the edge surface 13A directly enters into the activelayer 4. Thereby, the problem of increased optical path distance of theoptical beam is successfully eliminated.

On the other hand, such a construction also has a drawback in that mostpart of the optical beam emitted from the optical waveguide layer 13c,which typically has a thickness of about 6 μm, misses the active layer 4that has a thickness of only 2-3 μm. It should be noted that the opticalbeam emitted from the optical waveguide layer 13c has a sizecorresponding to the thickness of the layer 13c in the verticaldirection. In other words, the construction of FIG. 4 inherentlyprovides a large optical loss and cannot provide a satisfactory opticalcoupling.

In addition, the construction of FIG. 4 requires adjustment processbetween the photodetection device and the external optical waveguidelayer 13 on the substrate 1, for maximizing the optical coupling betweenthe active layer of the photoreception device 10 and the opticalwaveguide 13, while such an adjustment is complex and increases the costof the optical module.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful optical module as well as to a fabrication processthereof wherein the foregoing problems are eliminated.

Another and more specific object of the present invention is to providean optical module suitable for optimizing optical coupling between aphotoreception device and an optical waveguide, without carrying outcomplex adjustment process, such as the one that seeks for a maximum inthe output of the photodetection device.

Another object of the present invention is to provide an optical module,comprising:

a support substrate;

an optical waveguide provided on said support substrate for guiding anoptical beam therethrough;

a photoreception device provided on said support substrate, saidphotoreception device including a photodetection area that responds toan incoming optical beam;

optical path conversion means for converting an optical path of saidoptical beam guided through said optical waveguide and emittedtherefrom, from a first optical path to a second optical path that leadsto said photodetection area of said photoreception device;

said optical waveguide having an edge surface for emitting said opticalbeam guided through said optical waveguide, along said first opticalpath;

said photoreception device being provided on said support substrate soas to be hit by said optical beam emitted from said edge surface of saidoptical waveguide;

said optical path conversion means being formed on said photodetectiondevice as a part thereof, such that said optical beam emitted from saidedge surface of said optical waveguide impinges upon said photodetectionarea of said photoreception device.

According to the present invention, the optical path conversion means isformed on the photoreception device, which in turn is provided on thesupport substrate, commonly to the optical waveguide. Thereby, theoptical beam emitted from the optical waveguide hits the optical pathconversion means with reliability, and the optical beam thus entered tothe optical path conversion means hits the photodetection area of thephotoreception device also with reliability, even when there may be somediversion in the optical beam emitted from the edge surface of theoptical waveguide. Thereby, a high optical coupling is guaranteedbetween the optical waveguide and the photoreception device. As theoptical waveguide and the photoreception device are formed of separatemembers, the present invention achieves the desired high opticalcoupling by merely mounting the photoreception device on the supportsubstrate that already carries the optical waveguide as an integralbody. Thereby, the alignment between the photoreception device and theoptical waveguide can be achieved simply by using a marker, and complexadjustment process that typically includes the step of seeking for themaximum in the output of the photoreception device, can be eliminated.

Another object of the present invention is to provide a method forfabricating a photodetection module, comprising the steps of:

forming a layered body on a substrate such that said layered bodyincludes an active layer;

forming a plurality of photoreception regions on said layered body;

forming a V-shaped groove on said layered body by an etching process,such that said V-shaped groove separates one photoreception region fromanother photoreception region;

dividing said layered body along said groove to form a plurality ofphotoreception elements, such that each of said photoreception elementshas an oblique surface in correspondence to said V-shaped groove; and

disposing said photoreception device upon a support substrate carryingthereon an optical waveguide, such that said oblique surface faces anedge surface of said optical waveguide.

According to the present invention, each of the photoreception devicehas an oblique edge surface corresponding to the V-shaped groove, andthe oblique edge surface acts as a prism surface or mirror surface thatchanges the path of the optical beam emitted from the optical waveguideand entered the photoreception device, such that the optical beam hitsthe photodiode formed in the photoreception device. As the obliquesurface is formed integrally to the photoreception device as a partthereof, it is not necessary to adjust the position of the obliquesurface and the photodiode in the photoreception device. Further, as thephotoreception device is mounted directly upon the support substratecarrying the optical waveguide, the adjustment between thephotoreception device and the optical waveguide is substantiallyfacilitated.

Another object of the present invention is to provide a method forfabricating a semiconductor optical detection device, comprising thesteps of:

depositing a resist pattern on a substrate that carries thereon anactive layer, such that a photoreception region of said active layer isexposed;

depositing a conductor layer on said resist pattern such that saidconductor layer covers said exposed photoreception region;

depositing an electrode layer on said conductor layer by anelectroplating process while using said conductor layer as an electrode;and

forming an electrode lead by removing said resist pattern underneathsaid electrode layer.

According to the present invention, it is possible to form a leadelectrode such that the lead electrode extends parallel to the layeredbody forming the photoreception device with a separation therefrom, bycarrying out an electroplating process on the resist pattern, followedby removal of the resist pattern. The photoreception device having sucha lead electrode can be mounted on a support substrate in such a statethat the photoreception device engages with the support substrate at aside wall thereof and such that a principal surface of thephotoreception device extends perpendicularly to the support substrate.The foregoing lead electrode may be bent and connected to a conductorpattern formed on the support substrate. In such a case, the opticalbeam emitted from an edge surface of an optical waveguide provided onthe support substrate impinges upon the photoreception device generallyin the direction perpendicular to the foregoing principal surface andexperiences deflection toward a photodiode formed in the photoreceptiondevice by a prism surface formed on a part of the principal surface ofthe photoreception device. Thereby, the optical path length of theoptical beam emitted from the optical waveguide and reaching thephotodiode is reduced substantially, and the problem of spreading of theoptical beam at the photodiode is minimized.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the construction of a conventional opticalmodule;

FIG. 2 is a circuit diagram showing the equivalent circuit diagram ofthe optical module of FIG. 1;

FIG. 3 is a diagram showing the construction of another conventionaloptical module;

FIG. 4 is a diagram showing the construction of still anotherconventional optical module;

FIG. 5 is a diagram showing the construction of an optical moduleaccording to a first embodiment of the present invention;

FIG. 6 is a diagram showing the construction of an optical moduleaccording to a second embodiment of the present invention;

FIG. 7 is a diagram showing the optical module of FIG. 6 in a plan view;

FIG. 8 is a diagram showing a fabrication step of the optical module ofFIG. 6;

FIG. 9 is a diagram showing the construction of an optical moduleaccording to a third embodiment of the present invention;

FIG. 10 is a diagram showing the construction of an optical moduleaccording to a fourth embodiment of the present invention;

FIG. 11 is a diagram showing the construction of an optical moduleaccording to a fifth embodiment of the present invention;

FIG. 12 is a diagram showing the construction of an optical moduleaccording to a sixth embodiment of the present invention;

FIG. 13 is a diagram showing the construction of an optical moduleaccording to a seventh embodiment of the present invention;

FIG. 14 is a diagram showing the construction of an optical moduleaccording to an eighth embodiment of the present invention;

FIG. 15 is a diagram showing the construction of an optical moduleaccording to a ninth embodiment of the present invention;

FIGS. 16A-16H are diagrams showing the fabrication process of theoptical module of FIG. 15;

FIGS. 17A and 17B are diagrams showing various embodiments of a prismsurface used in the optical module of the present invention; and

FIG. 18 is a diagram showing the construction of an optical moduleaccording to a tenth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5 shows the construction of an optical module 200 according to afirst embodiment of the present invention.

Referring to FIG. 5, the optical module 200 is formed on a supportsubstrate 21 of Si, and includes an optical waveguide 22 formed on thesubstrate 21 and a photoreception device 20 formed also on the substrate21 such that a side wall of the photoreception device 20 faces an edgesurface 22A of the optical waveguide 22. The optical waveguide 22 isformed of glass or semiconductor layers deposited on the Si substrate 21by a CVD process and includes a lower cladding layer 22a, a core layer22b formed thereon, and an upper cladding layer 22c formed further onthe core layer 22b. The optical waveguide 22 may be coupled optically toanother optical waveguide (not shown) or a light emitting device on thesupport substrate 21 (not shown), wherein the optical waveguide 22guides the optical beam injected thereto and emits the same at theforegoing edge surface 22A.

The photoreception device 20, on the other hand, is formed on a devicesubstrate 23 of n-type InP and includes a buffer layer 24 of n-type InPcorresponding to the layer 3 of FIG. 1, an absorption layer 25 ofundoped InGaAs formed on the layer 24 in correspondence to the layer 4of FIG. 1, and an active layer 26 of n⁻ -type InP corresponding to thelayer 5 of FIG. 1, wherein the layer 26 includes a p-type region 26ahaving a first area and another p-type region 26b having a second,smaller area, respectively in correspondence to the drive diode D1 andthe photodiode D2 of FIG. 2. Further, electrode 27a and 27b are providedrespectively on the regions 26a and 26b.

It should be noted that the device substrate 23 is defined by a sidewall 23a and is provided on the support substrate 21 such that the sidewall 23a faces the edge surface 22A of the foregoing optical waveguide22. Further, the side wall 23a carries an anti-reflection film (notshown) thereon, and the side wall 23a and the edge surface 22A of theoptical waveguide are engaged with each other across such ananti-reflection film.

In the optical module 200 of FIG. 5, the device substrate 23 furtherincludes a depression defined by an oblique surface 23A on the lowermajor surface of the device substrate 23. Thus, there is formed a cavityor space 23B between the support substrate 21 and the device substrate23 in correspondence to the depression, wherein the oblique surface 23Adefining the depression forms an angle of θ₁ with respect to theprincipal surface of the support substrate 21. Thereby, the obliquesurface acts as a mirror surface that reflects the optical beam incidentthereto from the edge surface 22A of the optical waveguide 22 toward thep-type region 23b.

In order that the optical beam reflected by the mirror surface 23Acorrectly hits the p-type region 26b, the total thickness T of thelayered semiconductor body including the layers 23-26 is adjusted withrespect to the angle θ₁. When the oblique surface 23A is formed by a wetetching process of the device substrate 23, it should be noted that the(111) surface of InP appears as a result of the wet etching process. Inthis case, the angle θ₁ theoretically takes a value of 54.7°, which ispertinent to the (111) surface of InP. Generally, the angle θ₁ changessomewhat depending upon the type of the etchant or the mask pattern usedin the etching process. By using an aqueous solution of HCl, Br or HBr,one can expose the foregoing (111) surface at the mirror surface 23A,and the angle θ₁ takes a value of about 55°. In such a wet etchingprocess, it is also possible to use a solution of HCl and H₃ PO₄ orethanol that contains Br, for the etchant.

On the lower major surface of the device substrate 23, a flux layer 23Cis provided so as to include the oblique surface 23A, wherein the fluxlayer 23C typically includes layers of Ti, Au, Sn and Au respectivelywith thicknesses of 0.1 μm, 0.1 μm, 2 μm and 0.1 μm. By causing a fusionin the flux layer 23C in the state that the device substrate 23 isdisposed on the support substrate 21, the photoreception device 20 isfirmly bonded upon the support substrate 21. Thereby, the flux layer 23Ccovering the mirror surface 23A acts as a reflective coating thatreflects the optical beam incident to the device substrate 23 from theedge surface 22A of the optical waveguide 22.

In the illustrated example, the optical beam emitted from the edgesurface 22A of the optical waveguide 22 is reflected back in the upwarddirection by the mirror surface 23A. Thus, in correspondence to the pathof the reflected optical beam, the diffusion region 26b forming thephotodiode D2 is formed close to the side wall 23a with respect to thediffusion region 26a that forms the photodiode D1.

In the optical module 200 of FIG. 5 where the photoreception device 20is mounted upon the support substrate 21 that carries thereon theoptical waveguide 22 such that the lower major surface of thephotoreception device 20 engages with the upper major surface of thesupport substrate 21 and such that the side wall 23a of the devicesubstrate 23 engages with the edge surface 22A of the optical waveguide22, with the anti-reflection film intervening therebetween, it ispossible to achieve the desired high efficiently optical couplingbetween the photoreception device 20 and the optical waveguide 22 easilyby a simple mounting process of the photoreception device 20 on thesupport substrate 21. The alignment between the photoreception deviceand the optical waveguide is achieved easily by using a positioning markM as shown in FIG. 5.

In the construction of FIG. 5, it should be noted further that theoptical beam emitted from the edge surface 22A of the optical waveguide22 hits the diffusion region 26b forming the photodiode D2 of FIG. 2 aswell as associated depletion region, from the lower direction. Thereby,the entire optical beam spot falls upon the diffusion region 26b, andthe problem such as the optical beam partly misses the diffusion region26b does not occur. In other words, the optical module of FIG. 5 has anadvantageous feature of reduced optical loss.

In the structure of FIG. 5, it should be noted that the supportsubstrate 21 is by no means limited to Si, but any other suitablesemiconductor material such as InP or even a glass may be used for thesupport substrate 21.

FIG. 6 shows the construction of an optical module 300 according to asecond embodiment of the present invention.

Referring to FIG. 6, the optical module 300 includes the supportsubstrate 21 carrying thereon the optical waveguide 22 similarly to theembodiment of FIG. 5, wherein the support substrate 21 now carries aphotoreception device 30 that includes a device substrate 33 of n-typeInP. It will be noted that the device substrate 33 is defined by a sidewall 33a and includes an oblique surface 33A formed along the edge wherethe foregoing side wall 33a meets with a lower major surface 33b of thesubstrate 33, wherein the oblique surface 33A forms an angle of θ₂ withrespect to the lower major surface 33b of the device substrate 33.

Similarly as before, the device substrate 33 carries, on the upper majorsurface thereof, a buffer layer 34 of n-type InP corresponding to theInP layer 3 or 24, and an optical absorption layer 35 of undoped InGaAsis provided on the buffer layer 34 in correspondence to the opticalabsorption layer 4 or 25 described previously. Further, an active layer36 of n⁻ -type InP is provided on the layer 35 in correspondence to thelayer 5 or 26 described already, wherein the layer 36 includes a p-typeregion 35a corresponding to the photodiode D2 and a p-type region 36bcorresponding to the drive diode D2.

In the illustrated example, the lower major surface of the devicesubstrate 33 is jointed upon the upper major surface of the supportsubstrate 21 similarly to the first embodiment, and the device substrate33 is disposed such that the side wall 33a faces the edge surface 22A ofthe optical waveguide 22 and such that the optical beam emitted from theedge surface 22A of the optical waveguide 22 impinges upon the obliquesurface 33A of the device substrate 33.

In FIG. 6, it is illustrated that the edge surface 22A of the opticalwaveguide 22 and the side wall 33a of the device substrate 33 arealigned on a common plane, while the present embodiment is not limitedto such an embodiment, and one may provide the device substrate 33 suchthat the edge surface 22A of the optical waveguide 22 is located at aposition beyond the side wall 33a where the oblique surface 33A forms anoverhang. In such a construction, too, one can easily determine thepositional relationship between the device substrate 33 and the opticalwaveguide 22 by using the positioning mark M formed on the supportsubstrate 21.

In the optical module 300 of FIG. 6, it should be noted that theforegoing oblique surface 33A carries an anti-reflection film (notillustrated), and the optical beam emitted from the edge surface 22A ofthe optical waveguide 22 is reflected in the upward direction toward theupper major surface of the device substrate 33 at the foregoing obliquesurface 33A. Thereby, the optical beam thus refracted impinges upon thediffusion region 36a that forms the photodiode D2.

In order to receive the optical beam thus refracted by the obliquesurface 33A now acting as a prism surface, the photoreception device 30of FIG. 6 includes the diffusion region 36a forming the photodiode D2 atthe side away from the side wall 33a with respect to the diffusionregion 36b forming the drive diode D1.

In such a construction, too, the optical beam emitted from the edgesurface 22A of the optical waveguide 22 hits the diffusion region 36afrom the lower direction, and the problem of optical loss caused by theoptical beam missing the diffusion region 36a becomes minimum.

Similarly as before, the angle θ₂ of the oblique surface 33A withrespect to the lower major surface 33b of the device substrate 33 fallsin a range between 45°-60°. Particularly, the angle θ₂ takes a value of54.7° when the oblique surface 33A is formed by the (111) surface ofInP.

FIG. 7 shows the photoreception device 30 of the optical module 300shown in FIG. 6 in a plan view.

Referring to FIG. 7, it will be noted that the diffusion region 36aforming the photodiode D2 has an area substantially smaller than thediffusion region 36b forming the drive diode D1. Associated with thereduced area for the diffusion region 36a that forms the essential partof the photodiode D2, the photodiode D2 shows a very high speedresponse. Further, it should be noted that the optical beam, emittedfrom the edge surface 22A of the optical waveguide 22, reaches thephotodiode D2 after traveling through the device substrate 33 with areduced optical path distance as compared with the case of using aseparate mirror element as in the conventional construction of FIG. 3.Thereby, the optical beam divergence is held minimum, and one can reducethe size of the diffusion region 36a accordingly. The same argument asabove applies also to the first embodiment described with reference toFIG. 5. Typically, the diffusion region 26b or 36a may be formed to havean area smaller than one-tenth the area of the diffusion region 26a or36b.

In the optical module 200 of FIG. 6, it will be noted that the devicesubstrate 33 has another oblique surface 33A' also along an edge wherethe lower major surface 33b of the device substrate 33 meets withanother side wall 33a' that opposes the side wall 33a. Thephotoreception device 30 having such a structure has an additionaladvantageous feature in that it can be fabricated easily by forming aplurality of V-shaped grooves G₁ -G₄ on a substrate or wafer carryingthe layers 34-36 formed on the device substrate 33, in correspondence tothe foregoing oblique surfaces 33A and 33A' as indicated in FIG. 8,followed by cleaving the device substrate 33 at each of the grooves G₁-G₄.

Referring to FIG. 8, it will be noted that the illustrated layeredsemiconductor body includes device regions DEVICE 1, DEVICE 2 and DEVICE3 each in turn including the p-type diffusion regions 36a and 36b in then⁻ -type InP layer 36. Further, an anti-reflection film 38 is formed onthe lower major surface of the device substrate 33 including the groovesG₁ -G₄, wherein each of the photoreception device 30 is mounted upon thesupport substrate 21 by a flux layer at the lower major surface of thedevice substrate 33 as indicated in FIG. 6.

In any of the embodiments of FIGS. 5 and 6, it should be noted thatproper injection of the optical beam, emitted from the edge surface 22Aof the optical waveguide 22, into the diffusion region 26b or 36a thatforms the photodiode D2, depends primarily upon a proper location ofincidence of the optical beam into the oblique surface 22A or 33A andhence the relative height of the waveguide layer 22b with respect to thesemiconductor layers 25 and 26. On the other hand, the effect of thedistance D (FIG. 6) between the waveguide edge surface 22A and thedevice substrate 23 does not influence significantly upon such anoptical coupling between the optical waveguide 22 and the photodiode D2.

With this respect, the construction of FIG. 5 or FIG. 6 is particularlyadvantageous, as the device substrate 33 is mounted directly upon thesupport substrate 21, and because of the fact that the thickness of thesemiconductor layers 34-36 as well as the layers 22a-22c forming theoptical waveguide 22 can be controlled with high precision. Because itis not necessary to adjust the distance D with high precision, thecoarse adjustment using the marker M is sufficient for achieving thedesired optical coupling.

Next, an optical module 400 according to a third embodiment of thepresent invention will be described with reference to FIG. 9, whereinthose parts described previously are designated by the same referencenumerals and the description thereof will be omitted.

Referring to FIG. 9, the optical module 400 has a constructionsubstantially identical with the module 200 of FIG. 5, except that theoptical module 400 includes a curved mirror surface 23A' in place of theflat mirror surface 23A of FIG. 5. As a result of use of the curvedmirror surface 23A', it is possible to focus the reflected optical beamupon the diffusion region 26b forming the photodiode D2. Thereby, onecan reduce the area of the diffusion region 26b and hence the junctioncapacitance of the photodiode D2 further, and the response of thephotodiode D2 is improved.

It should be noted such a curved mirror surface 23A' can be formed by aprocess described in the U.S. Pat. No. 5,309,468, which is incorporatedas a reference. Briefly, the process employs a thermally inducedreflowing of a resist pattern that causes a blunting in the edge of theresist pattern, followed by a dry etching process while using such ablunted resist pattern as an etching mask.

As other aspects of the present embodiment are identical to those ofFIG. 5, further description of the present embodiment will be omitted.

FIG. 10 shows the construction of an optical module 500 according to afourth embodiment of the present invention, wherein those partsdescribed previously are designated by the same reference numerals andthe description thereof will be omitted.

Referring to FIG. 10, the optical module 500 has a constructionsubstantially identical with the module 300 of FIG. 6, except that theoptical module 500 includes a curved prism surfaces 33B and 33B' inplace of the flat prism surfaces 33A and 33A' of FIG. 6. As a result ofuse of the curved prism surfaces 33B and 33B', it is possible to focusthe refracted optical beam upon the diffusion region 36a forming thephotodiode D2. Thereby, one can reduce the area of the diffusion region36a and hence the junction capacitance of the photodiode D2 further, andthe response of the photodiode D2 is improved.

It should be noted such a curved prism surfaces 33B and 33B' can beformed by a process described in the U.S. Pat. No. 5,309,468 similarlyto the case of the curved mirror surfaces 23A'.

As other aspects of the present embodiment are identical to those ofFIG. 6, further description will be omitted.

FIG. 11 shows the construction of an optical module 600 according to afifth embodiment of the present invention, wherein those partscorresponding to the parts described previously are designated by thesame reference numerals and the description thereof will be omitted.

In the construction of FIG. 11, it will be noted that the photoreceptiondevice 20 of FIG. 6 is mounted upon the support substrate 21 in a turnedover state by a flip-chip process, such that the electrodes 27a and 27bare connected to the wiring patterns 21a and 21b formed on the supportsubstrate 21. For this purpose, the photoreception device 20 carriessolder bumps in correspondence to the electrodes 27a and 27b.

In the construction of FIG. 11, it will be noted that the mirror surface23A is now formed at the top side of the device substrate 23. Thus, theoptical module 600 of FIG. 11 provides a thick spacer layer 22B ofpolyimide on the support substrate 21 and forms an optical waveguide 22'thereon such that the optical beam emitted from an edge surface 22A' ofthe optical waveguide 22' hits the mirror surface 23A properly. Itshould be noted that the optical waveguide 22' includes a lower claddinglayer 22a' formed directly on the spacer layer 22B, an optical waveguidelayer 22b' formed on the cladding layer 22a' and an upper cladding layer22c' formed further on the optical waveguide layer 22b'. The opticalbeam thus reflected by the mirror surface 23A hits the diffusion region26b of the photodiode D2. In order to facilitate the reflection of theoptical beam, a reflective film 23C' is formed on the upper majorsurface of the device substrate 23 so as to cover the mirror surface23A.

As the photoreception device 20 is mounted upon the support substrate 21by a flip-chip process in the optical module 600 of FIG. 11, it is nolonger necessary to provide wire bonding process upon the electrodes 27aand 27b of the photoreception device 20. Thereby, the risk that thediffusion region 26b forming the essential part of the photodiode D2being damaged by a mechanical stress associated with the wire bondingprocess, is substantially reduced. Further, the use of the flip-chipprocess improves the throughput of production.

FIG. 12 shows the construction of an optical module 700 according to asixth embodiment of the present invention, wherein those parts describedpreviously are designated by the same reference numerals and thedescription thereof will be omitted.

In the construction of FIG. 12, the photoreception device 30 of FIG. 6is mounted upon the support substrate 21 in a turned over state by aflip-chip process, such that the electrodes 37a and 37b cause electricalas well as mechanical engagement with the wiring patterns 21a and 21bformed on the support substrate 21. Further, the optical waveguide 22'is provided on the support substrate in the state that the spacer layer22B is intervening between the support substrate 21 and the opticalwaveguide 22'. Thus, the optical beam emitting form the edge surface22A' of the optical waveguide 22' experiences a refraction in thedownward direction at the prism surface 33A now formed at the top sideof the support substrate 33 and hits the diffusion region 36a nowlocated at the bottom side of the device substrate 33 as indicated inFIG. 12.

In the construction of FIG. 12, too, it is possible to eliminate anymechanical stress from the photodiode D2 due to the flip-chip mountingprocess. Further, the throughput of fabrication of the optical module isimproved.

Next, an optical module 800 according to a seventh embodiment of thepresent invention will be described with reference to FIG. 13.

Referring to FIG. 13, the optical module 800 includes a photoreceptiondevice 30₁ having a construction similar to the photoreception device30, wherein the photoreception device 30₁ is flip-chip mounted upon thesupport substrate 21 similarly to the optical module 700 of FIG. 12. Onthe other hand, the photoreception device 30₁ includes the semiconductorlayers 34-36 on the bottom side of the device substrate 33. Further, thedevice substrate 33 includes an oblique surface 33C at the edge wherethe side wall 33a of the device substrate 33 and the surface of thesemiconductor layer 36 meet with each other. Thus, the optical beamemitted from the edge surface 22A of the optical waveguide 22, formed onthe support substrate 21, impinges straight upon the foregoing obliquesurface 33C acting as a prism surface, and the optical beam experiencesa refraction in the upward direction at the prism surface 33C.

It should be noted that the device substrate 33 includes a diffractiongrating 33X formed on the top side thereof in the illustrated,turned-over state of the photoreception device 30₁, such that theoptical beam, refracted by the prism surface 33C, experiences adiffraction. As a result of the diffraction, the optical beam isdecomposed into a number of optical beam elements each corresponding toan optical component included in the optical beam, in which the opticalcomponents are wavelength multiplexed.

The optical beam elements are thereby diffracted by the diffractiongrating 33X with respective diffraction angles according to thewavelengths thereof and reach the bottom side of the device substrate 33where the semiconductor layers 34-36 are formed.

In the optical module 800 of FIG. 13, the layer 36, formed of n⁻ -typeInP, includes a number of p-type diffusion regions (36a)₁, (36a)₂,(36a)₃, . . . , in correspondence to where the diffracted optical beamelements are expected to hit. Further, bump electrodes (37a)₁, (37a)₂,(37a)₃, . . . are provided in correspondence to the diffusion regions(36a)₁, (36a)₂, (36a)₃, . . . , wherein each of the diffusion regions(36a)₁, (36a)₂, (36a)₃, . . . forms a photodiode D2. The photoreceptiondevice 30₁ is flip-chip mounted upon the support substrate 21 such thatthe bump electrodes (37a)₁, (37a)₂, (37a)₃, . . . achieve electrical aswell as mechanical engagement with corresponding wiring patterns (21a)₁,(21a)₂, (21a)₃, . . . provided on the support substrate 21.

Thus, the optical module 800 of FIG. 13 not only achieves the desired,efficient optical coupling between the optical waveguide 22 and thephotodiode D2 with low cost, but also acts as an optical demultiplexerfor demultiplexing a wavelength-multiplex optical signal supplied fromthe optical waveguide 22.

Next, an optical module 900 according to an eighth embodiment of thepresent invention will be described with reference to FIG. 14, whereinthose parts corresponding to the parts described previously aredesignated by the same reference numerals and the description thereofwill be omitted.

Referring to FIG. 14, the optical module 900 is a modification of theoptical module 300 of FIG. 6 and includes a photoreception device 30₂where the semiconductor layer 34 in the photoreception device 30 is nowreplaced by a multilayer filter 34'. The multilayer filter 34' includesan alternate stacking of an InGaAsP film and an InP film each having aquarter wavelength thickness of the incident optical beam, and passesthe optical beam having a predetermined wavelength selectively to thephotodiode D2 after the optical beam is refracted by the prism surface33A. Thus, the optical module 900 operates as a wavelength-selectiveoptical detector.

Next, an optical module 1000 according to a ninth embodiment of thepresent invention will be described with reference to FIG. 15, whereinthose parts described previously are designated by the same referencenumerals and the description thereof will be omitted.

Referring to FIG. 15, the optical module 1000 includes a photoreceptiondevice 30₃ provided on the support substrate 21, in an upright statesuch that the side wall 33a now engages with the top surface of thesupport substrate 21. More specifically, the photoreception device 30₃is disposed on the device substrate 21 such that the principal surface33b of the device substrate 33 faces the optical waveguide 22.

Thus, the optical beam emitted from the optical waveguide 22 hits theoblique surface 33A acting as a prism surface and is refracted in theupward direction, wherein the optical beam thus refracted reaches thep-type diffusion region 36a formed at the other side of the devicesubstrate 33 and forming the photodiode D2.

The photoreception device 30₃ of FIG. 15 further includes an L-shapedlead electrode 39 in connection to the electrode 37a corresponding tothe diffusion region 36a, and the L-shaped lead electrode 39 isconnected to the wiring pattern 21a formed on the support substrate 21.It should be noted that such a connection of the lead electrode 39 tothe wiring pattern 21a is achieved easily by a surface mounting process.

In the optical module 1000 of FIG. 15, it should be noted that theoptical beam emitted from the edge surface 22A of the optical waveguide22 proceeds to the diffusion region 36a through the device substrate 33with a minimum optical path length. Thereby, the divergence of theoptical beam at the diffusion region 36a is held minimum.

When fabricating the optical module 1000 of FIG. 15, it is desired toform the lead electrode 39 on the photoreception device 30₃ by adeposition of a conductor layer rather than conducting a wire bondingprocess, so as to eliminate stress from the diffusion region 36a.

FIGS. 16A-16H show the process for forming the lead electrode 39,wherein FIG. 16B shows a plan view of the structure of FIG. 16A, FIG.16D shows a plan view of the structure of FIG. 16C, FIG. 16F shows aplan view of the structure of FIG. 16E, and FIG. 16H shows a plan viewof the structure of FIG. 16G.

FIGS. 16A and 16B show the photoreception device 30₃ in the initialstate in which the diffusion region 36a is formed in the layer 36 of n⁺-type InP, wherein FIG. 16A shows the cross section of the structure ofFIG. 16B taken along a line I-I'.

Next, in the step of FIGS. 16C and 16D, a polyimide layer 36₁ isdeposited on the InP layer 36, followed by a patterning process using aresist mask 36₂, to expose the diffusion region 36a. Further, anelectrode layer 37 is deposited on the resist mask 36₂ so as to coverthe exposed surface of the diffusion region 36a, by depositing layers ofTi, Pt and Au consecutively. Thereby, the Au layer acts as a lowresistance layer while the Ti and Pt layers act as a barrier metallayer.

Next, in the step of FIGS. 16E and 16F, a resist pattern 39a is formedso as to expose the region where the lead electrode 39 is to be formed,and the lead electrode 39 is formed on the exposed part of the electrodelayer 37 by an electrode plating process of Au.

After the lead electrode 39 is formed as such, the electrode layer 37outside the lead electrode 39 is removed by an ion milling process.Further, by removing the resist patterns 39a and 36₂ by dissolving theresin of the resist patterns into a solvent, a structure shown in FIGS.16G and 16H is obtained. In the structure of FIGS. 16G and 16H, it willbe noted that lead electrode 39 extends along the surface of thesemiconductor layer 36 but with a separation therefrom. Further, ascribe line 33Z is formed on the rear side of the device substrate 33for facilitating the cleaving process used for dividing the structureinto individual photoreception devices.

FIGS. 17A and 17B show a modification of the prism surface 33A formed onthe device substrate 33.

In the example of FIG. 17A, it will be noted that the prism surface 33Ais formed only on a part of the ridge where the side wall 33a meets thelower major surface of the support substrate 33, while the prism surfaceof FIG. 17B extends over the entire length of the foregoing ridge.

Any of the constructions of FIG. 17A and FIG. 17B may be employed forthe photodiode with the same effect in terms of the function of thedevice, while the construction of FIG. 17A may be more preferable inview of the rigidity of the substrate when forming a large number ofsuch photodiodes on a common substrate or wafer. In the construction ofFIG. 17B, the mechanical strength of the wafer may be deteriorated dueto the grooves formed on the wafer in large number.

FIG. 18 shows the construction of an optical module 1100 according to atenth embodiment of the present invention.

Referring to FIG. 18, the optical module 1100 includes the supportsubstrate 21 that carries thereon the photoreception device 30 similarlyto the optical module 300 of FIG. 6, except that the support substrate21V is formed with a V-shaped groove 21 on the principal surface thereoffor engagement with an optical fiber 220 that includes an optical core221.

In such a structure, the optical beam in the core 221 impinges upon theprism surface 33A of the device substrate 33 and experiences arefraction similarly to the case of the optical module 300 of FIG. 6,wherein the optical beam thus refracted hits the diffusion region 36aforming the photodiode D2. It should be noted that such a V-shapedgroove is formed easily on a Si substrate by a well known etchingprocess that uses KOH as an etchant. In this case, the V-shaped grooveis defined by a pair of crystal surfaces of Si.

Further, the present invention is not limited to the embodimentsdescribed heretofore, but various variations and modifications may bemade without departing from the scope of the invention.

What is claimed is:
 1. A method for fabricating a photodetection module,comprising the steps of:forming a layered body on a top surface asubstrate such that said layered body includes an active layer; forminga plurality of photoreception region on said layered body; forming aV-shaped groove on a bottom surface of said substrate by an etchingprocess, such that said V-shaped groove separates one photoreceptionregion from another photoreception region; dividing said layered bodyand said substrate along said V-shaped groove by a cleaving process toform a plurality of photoreception elements, such that each of saidphotoreception elements has an oblique surface in correspondence to sidewalls of said V-shaped groove; and disposing said photoreception deviceupon a support substrate carrying thereon an optical waveguide, suchthat said oblique surface faces an edge surface of said opticalwaveguide.
 2. A method as claimed in claim 1, wherein said etchingprocess is conducted by a wet etching process such that said V-shapedgroove is defined by a pair of crystal surfaces.